In recent years, in a construction machine represented by a hydraulic excavator, many equipment devices configured to perform electronic control have been adopted for a reduction on fuel consumption and an improvement on controllability. There is known a method in which a control valve for controlling main actuators (for example, hydraulic cylinders and hydraulic motors) in the construction machine is remote-controlled by a hydraulic pressure (that is, a pilot pressure) controlled with a solenoid type pressure reducing valve unit described in Patent Document 1, for example.
In the solenoid type pressure reducing valve unit according to such a conventional art, a main spool receives a pilot pressure (controlled primary pressure) controlled in pressure in proportion to a supply electric current. As a result, the main spool is moved in an axial direction. The movement of the main spool causes communication and blocking between a primary pressure port and an output port, thus repeatedly performing the communication and blocking between the output port and a main drain passage (tank port). As a result, a pressure of the output port is controlled as a controlled secondary pressure to the controlled primary pressure in such a manner as to produce balance between a load (for example, a force that pushes the spool in one direction) by the controlled primary pressure (pilot pressure), and a load (for example a force that pushes the spool in the other direction) by the pressure of the output port and an urging force of a spring (elastic body such as a return spring).